JP2018099160A - Golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a golf ball by which a distance can be easily made to match in putting and excellent in approach performance.SOLUTION: A golf ball comprises a core and a cover positioned outside the core. A difference (FB-FC) between a secondary natural frequency of a golf ball FBand a secondary natural frequency of a core FCis larger than 420 Hz and equal to or less than 760 Hz. Preferably, the golf ball has a sum (FB+FC) of 5200 Hz or less. Preferably, the FCis 1700 Hz or more and 2400 Hz or less. Preferably, the FBis 2250 Hz or more and 3050 Hz or less. Preferably, a compressive deformation amount Dc of the core is 2.30 mm or more and 3.90 mm or less. Preferably, the golf ball has a compressive deformation amount Db of 1.80 mm or more and 3.30 mm or less. A thickness Tc of the cover is preferably 1.00 mm or more and 2.30 mm or less. A shore D hardness Hc of the cover is preferably 54 or more and 67 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a golf ball. Specifically, the present invention relates to a golf ball having a core and a cover.

  In golf, a golf ball is hit by a wood type club, an iron type club, a hybrid type club (utility), a putter or the like. The hit feeling at the time of hitting is a player's concern. Generally, players want a golf ball with a soft feel at impact. Japanese Patent Application Laid-Open No. 11-76461 proposes improvement of the hit feeling with a wood type golf club.

  In beginner play, the frequency of miss shots is high. Accordingly, the beginner is insensitive to the feel of hitting a golf ball with a wood type club, iron type club or hybrid type club.

  On the other hand, in putting, even a beginner often hits a golf ball at a sweet spot of a putter. Even beginners are sensitive to the feeling of hitting in putting. Beginners prefer golf balls that provide a soft feel when put. Japanese Patent Application Laid-Open No. 2000-317016 proposes a golf ball that produces a soft sound and feel when hit with a putter by adjusting the PGA compression of the core and the hardness of the cover.

JP-A-11-76461 JP 2000-317016 A

  In beginner play, the frequency of miss shots during putting is also high. In a golf ball with a soft feel at impact, the response at the time of impact is too small, and it may be difficult to grasp the sense of distance. In particular, in putting where the distance between the golf ball and the cup is long, it is often feared that the golf ball will be left behind, and the golf ball is hit with an unnecessarily strong force. There is a demand for a golf ball that has an appropriate feel at the time of putting and is easy to match the sense of distance.

  On the other hand, golf players place importance on the spin performance of golf balls. A golf ball that is easily spun when hit is excellent in controllability. In general, a hard golf ball has a high spin rate when hit with a wedge. This golf ball is excellent in controllability in approach shots, but gives a hard shot feeling when putting. There is still room for improvement in achieving both approach performance and feel at impact.

  An object of the present invention is to provide a golf ball that maintains the approach performance and easily adjusts the sense of distance, particularly in long-distance putting.

  The present inventors have found that the secondary natural frequency of the core and the golf ball affects the feel at impact, and proposed a golf ball having an excellent feel at impact when putting in Japanese Patent Application No. 2015-242909 filed earlier. doing. As a result of further studies, the present inventors have found that the secondary natural frequency of the core and the golf ball can also contribute to an improvement in the sense of distance during putting, thereby completing the present invention.

The golf ball according to the present invention includes a core and a cover positioned outside the core. When the secondary natural frequency of the golf ball is FB ₂ and the secondary natural frequency of the core is FC ₂ , the difference (FB ₂ −FC ₂ ) is greater than 420 Hz and 760 Hz or less.

Preferably, the sum (FB ₂ + FC ₂ ) of FB ₂ and FC ₂ is 5200 Hz or less.

Preferably, this FC ₂ is 1700 Hz or more and 2400 or less. Preferably, the FB ₂ is 2250 Hz to 3050 Hz.

  Preferably, the amount of compressive deformation Dc of the core is not less than 2.30 mm and not more than 3.90 mm. Preferably, the golf ball has a compression deformation amount Db of 1.80 mm or more and 3.30 mm or less.

  Preferably, the thickness Tc of the cover is not less than 1.00 mm and not more than 2.30 mm. Preferably, the Shore D hardness Hc of this cover is 54 or more and 67 or less.

In the golf ball according to the present invention, the difference (FB ₂ −FC ₂ ) is greater than 420 Hz and not greater than 760 Hz. This difference (FB ₂ −FC ₂ ) is large. The golf ball putter feel is appropriate. According to this golf ball, even a beginner can adjust the sense of distance when putting. Therefore, even when the distance to the cup is long, the occurrence of overshooting can be avoided. Furthermore, this golf ball is excellent in approach performance.

FIG. 1 is a cross-sectional view illustrating a golf ball according to an embodiment of the present invention. FIG. 2 is a conceptual diagram showing an apparatus for measuring the natural frequency of the golf ball of FIG. FIG. 3 is a graph in which the secondary natural frequency FB ₂ of the golf ball and the secondary natural frequency FC _{2 of the} core are plotted for the example and the comparative example.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  A golf ball 2 shown in FIG. 1 includes a spherical core 4 and a cover 6 positioned outside the core 4. In this embodiment, the cover 6 is directly joined to the core 4. This golf ball 2 is a so-called two-piece ball. The golf ball 2 has a plurality of dimples 8 on the surface thereof. A portion of the surface of the golf ball 2 other than the dimples 8 is a land 10. The golf ball 2 includes a paint layer and a mark layer outside the cover 6, but these layers are not shown.

  The golf ball 2 preferably has a diameter of 40 mm or greater and 45 mm or less. The diameter is particularly preferably equal to or greater than 42.67 mm from the viewpoint that US Golf Association (USGA) standards are satisfied. In light of suppression of air resistance, the diameter is more preferably equal to or less than 44 mm, and particularly preferably equal to or less than 42.80 mm. The golf ball 2 preferably has a mass of 40 g or more and 50 g or less. In light of attainment of great inertia, the mass is more preferably equal to or greater than 44 g, and particularly preferably equal to or greater than 45.00 g. In light of satisfying the USGA standard, the mass is particularly preferably equal to or less than 45.93 g.

  The core 4 is formed by crosslinking a rubber composition. Examples of preferable base rubber include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. Polybutadiene is preferred. When polybutadiene and other rubber are used in combination, it is preferable that polybutadiene is a main component. Specifically, the ratio of polybutadiene to the total base rubber is preferably 50% by mass or more, and particularly preferably 80% by mass or more. Polybutadiene having a cis-1,4 bond ratio of 80% or more is particularly preferable.

  The rubber composition of the core 4 preferably contains a co-crosslinking agent. A preferred co-crosslinking agent from the viewpoint of the resilience performance of the golf ball 2 is a monovalent or divalent metal salt of an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Preferred examples of the co-crosslinking agent include zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. From the viewpoint of the resilience performance of the golf ball 2, zinc acrylate and zinc methacrylate are particularly preferable.

  The rubber composition may contain an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms and a metal oxide. Both react in the rubber composition to obtain a salt. This salt functions as a co-crosslinking agent. Preferred α, β-unsaturated carboxylic acids include acrylic acid and methacrylic acid. Preferred metal oxides include zinc oxide and magnesium oxide.

  The amount of the co-crosslinking agent is preferably 10 parts by mass or more with respect to 100 parts by mass of the base rubber. The golf ball 2 having the core 4 whose amount is 10 parts by mass or more is excellent in resilience performance and easily matches the sense of distance when putting. In this respect, the amount is more preferably equal to or greater than 15 parts by weight, and particularly preferably equal to or greater than 20 parts by weight.

  The amount of the co-crosslinking agent is preferably 45 parts by mass or less with respect to 100 parts by mass of the base rubber. The golf ball 2 having the core 4 whose amount is equal to or less than 45 parts by mass is excellent in approach performance and has a soft feel at the time of putting. In this respect, the amount is more preferably equal to or less than 40 parts by weight, and particularly preferably equal to or less than 35 parts by weight.

  Preferably, the rubber composition of the core 4 includes an organic peroxide. The organic peroxide functions as a crosslinking initiator. The organic peroxide contributes to the resilience performance and feel at impact of the golf ball 2. Suitable organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butyl). Peroxy) hexane and di-t-butyl peroxide are exemplified. A particularly versatile organic peroxide is dicumyl peroxide.

  The amount of the organic peroxide is preferably 0.1 parts by mass or more with respect to 100 parts by mass of the base rubber. The golf ball 2 having the core 4 whose amount is equal to or greater than 0.1 parts by mass is excellent in resilience performance and easily matches the sense of distance when putting. In this respect, the amount is more preferably equal to or greater than 0.3 parts by weight, and particularly preferably equal to or greater than 0.5 parts by weight.

  The amount of the organic peroxide is preferably 3.0 parts by mass or less with respect to 100 parts by mass of the base rubber. The golf ball 2 having the core 4 whose amount is equal to or less than 3.0 parts by mass is excellent in approach performance and soft in hitting feeling at the time of putting. In this respect, the amount is more preferably equal to or less than 2.5 parts by weight, and particularly preferably equal to or less than 2.0 parts by weight.

  The rubber composition of the core 4 contains an organic sulfur compound. Organic sulfur compounds include naphthalene thiol compounds, benzene thiol compounds and disulfide compounds.

  As naphthalenethiol compounds, 1-naphthalenethiol, 2-naphthalenethiol, 4-chloro-1-naphthalenethiol, 4-bromo-1-naphthalenethiol, 1-chloro-2-naphthalenethiol, 1-bromo-2-naphthalene Examples include thiol, 1-fluoro-2-naphthalene thiol, 1-cyano-2-naphthalene thiol and 1-acetyl-2-naphthalene thiol.

  As benzenethiol compounds, benzenethiol, 4-chlorobenzenethiol, 3-chlorobenzenethiol, 4-bromobenzenethiol, 3-bromobenzenethiol, 4-fluorobenzenethiol, 4-iodobenzenethiol, 2,5-dichlorobenzenethiol 3,5-dichlorobenzenethiol, 2,6-dichlorobenzenethiol, 2,5-dibromobenzenethiol, 3,5-dibromobenzenethiol, 2-chloro-5-bromobenzenethiol, 2,4,6-tri Chlorobenzenethiol, 2,3,4,5,6-pentachlorobenzenethiol, 2,3,4,5,6-pentafluorobenzenethiol, 4-cyanobenzenethiol, 2-cyanobenzenethiol, 4-nitrobenzenethiol and 2 -Nito Benzenethiol are exemplified.

  Disulfide compounds such as diphenyl disulfide, bis (4-chlorophenyl) disulfide, bis (3-chlorophenyl) disulfide, bis (4-bromophenyl) disulfide, bis (3-bromophenyl) disulfide, bis (4-fluorophenyl) disulfide Bis (4-iodophenyl) disulfide, bis (4-cyanophenyl) disulfide, bis (2,5-dichlorophenyl) disulfide, bis (3,5-dichlorophenyl) disulfide, bis (2,6-dichlorophenyl) disulfide, bis (2,5-dibromophenyl) disulfide, bis (3,5-dibromophenyl) disulfide, bis (2-chloro-5-bromophenyl) disulfide, bis (2-cyano-5-bromophenyl) disulfide Bis (2,4,6-trichlorophenyl) disulfide, bis (2-cyano-4-chloro-6-bromophenyl) disulfide, bis (2,3,5,6-tetrachlorophenyl) disulfide, bis (2,3 , 4,5,6-pentachlorophenyl) disulfide and bis (2,3,4,5,6-pentabromophenyl) disulfide.

  From the viewpoint of the resilience performance of the golf ball 2 and the sense of distance when putting, the amount of the organic sulfur compound is preferably 0.1 parts by mass or more, particularly 0.2 parts by mass or more, with respect to 100 parts by mass of the base rubber. preferable. From the viewpoint of approach performance and feel at impact, this amount is preferably 1.5 parts by mass or less, more preferably 1.0 part by mass or less, and particularly preferably 0.8 part by mass or less. Two or more organic sulfur compounds may be used in combination.

  The rubber composition of the core 4 may contain a filler for the purpose of adjusting specific gravity and the like. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate, and magnesium carbonate. The amount of the filler is appropriately determined so that the intended specific gravity of the core 4 is achieved.

  This rubber composition may contain an appropriate amount of various additives such as sulfur, carboxylic acid, carboxylate, anti-aging agent, colorant, plasticizer, and dispersant. This rubber composition may contain a crosslinked rubber powder or a synthetic resin powder.

  The diameter of the core 4 is preferably 38.0 mm or more. In the golf ball 2 having the core 4 having a diameter of 38.0 mm or more, the cover 6 is thin. In this golf ball 2, the core 4 can contribute to the feel at impact when putting. The feel at impact of the golf ball 2 is soft. From these viewpoints, the diameter is more preferably 38.3 mm or more, and particularly preferably 38.5 mm or more. In light of durability and approach performance of the golf ball 2, the diameter is preferably 41.0 mm or less, more preferably 40.5 mm or less, and particularly preferably 40.0 mm or less.

  The compression deformation amount Dc of the core 4 is preferably 2.30 mm or more. In the core 4 in which the amount of compressive deformation Dc is 2.30 mm or more, the shot feeling at the time of putting is soft. In this respect, the amount of compressive deformation Dc is more preferably equal to or greater than 2.40 mm, and particularly preferably equal to or greater than 2.50 mm. From the viewpoint that an appropriate response can be obtained at the time of putting, the amount of compressive deformation Dc is preferably 3.90 mm or less, more preferably 3.80 mm or less, and particularly preferably 3.70 mm or less.

  A YAMADA compression tester is used to measure the amount of compressive deformation. In this tester, a sphere (core 4 or golf ball 2) is placed on a metal rigid plate. A metal cylinder gradually descends toward this sphere. The sphere sandwiched between the bottom surface of the cylinder and the rigid plate is deformed. The moving distance of the cylinder from the state where the initial load of 98 N is applied to the sphere to the state where the final load of 1274 N is applied is measured. The moving speed of the cylinder until the initial load is applied is 0.83 mm / s. The moving speed of the cylinder from the initial load to the final load is 1.67 mm / s.

  The difference (Hs−Ho) between the Shore C hardness Hs of the surface and the Shore C hardness Ho of the center in the core 4 is preferably 30 or less. The core 4 having a difference (Hs−Ho) of 30 or less does not excessively suppress the spin performance of the golf ball 2. The core 4 can contribute to the approach performance of the golf ball 2. In this respect, the difference (Hs−Ho) is more preferably equal to or less than 28, and particularly preferably equal to or less than 25. From the viewpoint of the flight performance of the golf ball 2, the difference (Hs−Ho) is preferably 12 or more, more preferably 13 or more, and particularly preferably 15 or more.

  In light of durability and approach performance, the central hardness Ho is preferably 55 or greater, more preferably 58 or greater, and particularly preferably 60 or greater. In light of feel at impact, the hardness Ho is preferably equal to or less than 80, more preferably equal to or less than 75, and particularly preferably equal to or less than 70.

  The hardness Ho is measured by a Shore C type hardness meter attached to an automatic hardness meter (trade name “Digitest II” of H. Burleys Co.). This hardness meter is pressed against the center of the cross-section of the hemisphere obtained by cutting the golf ball 2. The measurement is performed in an environment of 23 ° C.

  From the viewpoint of approach performance, the surface hardness Hs is preferably 75 or more, more preferably 78 or more, and particularly preferably 80 or more. In light of durability and feel at impact of the golf ball 2, the hardness Hs is preferably 95 or less, more preferably 90 or less, and particularly preferably 88 or less.

  The hardness Hs is measured by a Shore C type hardness meter attached to an automatic hardness meter (trade name “Digitest II” of H. Burleys Co.). This hardness meter is pressed against the surface of the core 4. The measurement is performed in an environment of 23 ° C.

  The mass of the core 4 is preferably 10 g or greater and 42 g or less. The crosslinking temperature of the core 4 is 140 ° C. or higher and 180 ° C. or lower. The crosslinking time of the core 4 is 10 minutes or more and 60 minutes or less.

  The cover 6 is located outside the core 4. The cover 6 is the outermost layer except for the mark layer and the paint layer. The cover 6 may be composed of two or more layers. Another layer may be provided between the cover 6 and the core 4.

  The cover 6 is formed from a thermoplastic resin composition. Examples of the base polymer of the resin composition include ionomer resins, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, thermoplastic polyurethane elastomers, thermoplastic polyolefin elastomers, and thermoplastic polystyrene elastomers. Ionomer resins are preferred. The ionomer resin is highly elastic. The cover 6 affects the feeling of hitting and the feeling of distance when putting. The golf ball 2 having the cover 6 containing an ionomer resin can give an appropriate response when putting. The cover 6 may be molded from a thermosetting resin composition.

  An ionomer resin and another resin may be used in combination. When used in combination, the ionomer resin is the main component of the base polymer from the viewpoint of feel at impact and distance when putting. The ratio of the ionomer resin to the total base polymer is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 85% or more.

  A preferable ionomer resin includes a binary copolymer of an α-olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. A preferable binary copolymer contains 80% by mass or more and 90% by mass or less α-olefin and 10% by mass or more and 20% by mass or less α, β-unsaturated carboxylic acid. As another preferable ionomer resin, a ternary copolymer of an α-olefin, an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α, β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms is used. A polymer is mentioned. Preferred terpolymers are 70% to 85% by weight α-olefin, 5% to 30% by weight α, β-unsaturated carboxylic acid, and 1% to 25% by weight. α, β-unsaturated carboxylic acid ester. In the binary copolymer and ternary copolymer, preferred α-olefins are ethylene and propylene, and preferred α, β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. A particularly preferred ionomer resin is a copolymer of ethylene and acrylic acid. Another particularly preferred ionomer resin is a copolymer of ethylene and methacrylic acid.

  In the binary copolymer and ternary copolymer, some of the carboxyl groups are neutralized with metal ions. Examples of the metal ions for neutralization include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions. Neutralization may be performed with two or more metal ions. Particularly suitable metal ions from the viewpoint of resilience performance and durability of the golf ball 2 are sodium ion, zinc ion, lithium ion and magnesium ion.

  As specific examples of the ionomer resin, trade names “Hi-Milan 1555”, “Hi-Milan 1557”, “Hi-Milan 1605”, “Hi-Milan 1706”, “Hi-Milan 1856”, “Hi-Milan 1856”, “Hi-Milan 1855” “Himiran AM7311”, “Himiran AM7315”, “Himiran AM7317”, “Himiran AM7329” and “Himiran AM7337”; DuPont's trade names “Surlin 6120”, “Surlin 6910”, “Surlin 7930”, “Surlin 7940”, “Surling 8140”, “Surling 8150”, “Surling 8940”, “Surling 8945”, “Surling 9120”, “Surling 9150”, “Surling 9910”, “Surling 9945”, “Surry AD8546 "," HPF1000 "and" HPF2000 "; and ExxonMobil Chemical Co. under the trade name of" IOTEK7010 "," IOTEK7030 "," IOTEK7510 "," IOTEK7520 "includes" IOTEK8000 "and" IOTEK8030 ". Two or more ionomer resins may be used in combination.

  The resin composition of the cover 6 may include a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer includes a polystyrene block as a hard segment and a soft segment. A typical soft segment is a diene block. Examples of the diene block compound include butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferred. Two or more compounds may be used in combination.

  The styrene block-containing thermoplastic elastomer includes styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS), SBS hydrogenated, SIS hydrogenated and SIBS hydrogenated are included. As a hydrogenated product of SBS, styrene-ethylene-butylene-styrene block copolymer (SEBS) can be mentioned. As a hydrogenated product of SIS, styrene-ethylene-propylene-styrene block copolymer (SEPS) can be mentioned. As a hydrogenated product of SIBS, styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS) can be mentioned.

  In light of the resilience performance of the golf ball 2, the content of the styrene component in the styrene block-containing thermoplastic elastomer is preferably 10% by mass or more, more preferably 12% by mass or more, and particularly preferably 15% by mass or more. In light of the feel at impact of the golf ball 2, the content is preferably equal to or less than 50% by mass, more preferably equal to or less than 47% by mass, and particularly preferably equal to or less than 45% by mass.

  In the present invention, the styrene block-containing thermoplastic elastomer includes an alloy of one or more selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS and SEEPS, and an olefin. The olefin component in the alloy is presumed to contribute to the improvement of compatibility with other base polymers. This alloy can contribute to the resilience performance of the golf ball 2. Olefins having 2 to 10 carbon atoms are preferred. Suitable olefins include ethylene, propylene, butene and pentene. Ethylene and propylene are particularly preferred.

  Specific examples of polymer alloys include Mitsubishi Chemical's trade names “Lavalon T3221C”, “Lavalon T3339C”, “Lavalon SJ4400N”, “Lavalon SJ5400N”, “Lavalon SJ6400N”, “Lavalon SJ7400N”, “Lavalon SJ8400N”, “Lavalon” SJ9400N "and" Lavalon SR04 ". Other specific examples of the styrene block-containing thermoplastic elastomer include Daicel Chemical Industries' trade name “Epofriend A1010” and Kuraray's trade name “Septon HG-252”.

  From the viewpoint of feel at impact when putting, the ratio of the styrene block-containing thermoplastic elastomer to the total base polymer is preferably 2% by mass or more, more preferably 4% by mass or more, and particularly preferably 6% by mass or more. From the viewpoint that it is easy to match the sense of distance during putting, this ratio is preferably 30% by mass or less, more preferably 25% by mass or less, and particularly preferably 20% by mass or less.

  The resin composition of the cover 6 may contain an appropriate amount of a colorant, a filler, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent whitening agent, and the like. When the color of the golf ball 2 is white, a typical colorant is titanium dioxide.

  The thickness Tc of the cover 6 is preferably 2.30 mm or less. The cover 6 having a thickness Tc of 2.30 mm or less does not hinder a soft shot feeling at the time of putting. In this respect, the thickness Tc is more preferably equal to or less than 2.20 mm, and particularly preferably equal to or less than 2.10 mm. In light of durability and approach performance of the golf ball 2, the thickness Tc is preferably equal to or greater than 1.00 mm, more preferably equal to or greater than 1.10 mm, and particularly preferably equal to or greater than 1.20 mm. The thickness Tc is measured immediately below the land 10.

  From the viewpoint that it is easy to match the sense of distance during putting, the Shore D hardness Hc of the cover 6 is preferably 54 or more, more preferably 55 or more, and particularly preferably 56 or more. From the viewpoint of feel at impact when putting, the hardness Hc is preferably 67 or less, more preferably 66 or less, and particularly preferably 65 or less.

  The hardness Hc of the cover 6 is measured in accordance with the regulations of “ASTM-D 2240-68”. The hardness H2 is measured by a Shore D type hardness meter attached to an automatic hardness meter (trade name “Digitest II” of H. Burleys). For the measurement, a sheet made of the same material as that of the cover 6 and having a thickness of about 2 mm formed by hot pressing is used. Prior to measurement, the sheet is stored at a temperature of 23 ° C. for 2 weeks. At the time of measurement, three sheets are overlaid.

  The compression deformation amount Db of the golf ball 2 is preferably 1.80 mm or more. In the golf ball 2 in which the amount of compressive deformation Db is 1.80 mm or more, the shot feeling at the time of putting is soft. In this respect, the amount of compressive deformation Db is more preferably equal to or greater than 1.90 mm, and particularly preferably equal to or greater than 2.00 mm. From the viewpoint that it is easy to match the sense of distance during putting, the amount of compressive deformation Db is preferably 3.30 mm or less, more preferably 3.20 mm or less, and particularly preferably 3.10 mm or less.

  FIG. 2 shows an apparatus for measuring the natural frequency of the core 4 and the golf ball 2. This apparatus has a vibrator 12, a plate 14, a first acceleration pickup 16, and a second acceleration pickup 18. The plate 14 is attached to the shaker 12. A sphere (core 4 or golf ball 2) is placed on the plate 14. The first acceleration pickup is attached to the plate 14. The second acceleration pickup 18 is attached to a sphere. Vibration is applied to the sphere by the vibrator 12. A signal of acceleration applied to the sphere is output from the first acceleration pickup 16. From the second acceleration pickup 18, a signal of the acceleration of the sphere is output. These signals are input to the dynamic signal analyzer. By the calculation of the analyzer, a curve showing the relationship between the frequency and the mechanical impedance in the sphere is obtained. The frequency at the minimum point of this curve is the natural frequency. The frequency at the minimal point appearing first in the curve is the primary natural frequency. The frequency at the minimum point that appears second in the curve is the secondary natural frequency. A typical shaker 12 is a trade name “PET” of International Institute of Mechanical Vibration. A typical dynamic signal analyzer is the trade name “HP-5420A” of Yokogawa Hewlett-Packard Company.

As a result of intensive studies, the inventors have approached when the secondary natural frequency FC ₂ (Hz) of the core 4 and the secondary natural frequency FB ₂ (Hz) of the golf ball 2 satisfy a predetermined relationship. It was found that while maintaining the performance, it is possible to obtain an appropriate shot feeling that is easy to match the sense of distance when putting. In particular, even when the distance to the cup is long, it is possible to avoid the occurrence of overshooting.

FIG. 3 is a graph showing the relationship between the secondary natural frequency FC ₂ of the core 4 and the secondary natural frequency FB ₂ of the golf ball 2. In this graph, the horizontal axis is the secondary natural frequency FC ₂ of the core, and the vertical axis is the secondary natural frequency FB ₂ of the golf ball. The broken line shown in this graph is expressed by the following (Formula 1).
FB ₂ = FC ₂ + 420 (Formula 1)
In this graph, in the zone above the broken line indicated by (Expression 1), the difference between the secondary natural frequency FB ₂ of the golf ball 2 and the secondary natural frequency FC ₂ of the core 4 (FB ₂ −FC ₂ ). However, it exceeds 420 Hz.

According to the knowledge obtained by the present inventor, the golf ball 2 having a difference (FB ₂ −FC ₂ ) larger than 420 Hz has an appropriate shot feeling at the time of putting. In this golf ball 2, the response obtained by the player who hit with the putter is relatively large. For this reason, even a beginner who has a long distance to the cup and is afraid of hitting the ball can hit the golf ball 2 with a weaker force than usual, so that overshooting can be avoided. From the viewpoint that it is easy to match the sense of distance during putting, the difference (FB ₂ −FC ₂ ) is more preferably 440 Hz or more, and further preferably 460 Hz or more.

The solid line shown in the graph of FIG. 3 is expressed by the following (formula 2).
FB ₂ = FC ₂ +760 (Formula 2)
In this graph, in the zone below the straight line represented by (Equation 2), the difference (FB ₂ −FC ₂ ) between the secondary natural frequency FB ₂ of the golf ball 2 and the secondary natural frequency FC ₂ of the core 4. Is 760 Hz or less. When the golf ball 2 having a difference (FB ₂ −FC ₂ ) of 760 Hz or less is hit with a wedge, the spin rate is high. This golf ball 2 is excellent in approach performance. From the viewpoint of approach performance, the difference (FB ₂ −FC ₂ ) is more preferably 740 Hz or less, and further preferably 720 Hz or less.

The sum (FB ₂ + FC ₂ ) of the secondary natural frequency FB _{2 of the} golf ball 2 and the secondary natural frequency FC ₂ of the core 4 is preferably 5200 Hz or less. In the golf ball 2 having a sum (FB ₂ + FC ₂ ) of 5200 Hz or less, the shot feeling at the time of putting is soft. In this respect, the sum (FB ₂ + FC ₂ ) is more preferably equal to or less than 5100 Hz, and further preferably equal to or less than 5000 Hz. The sum (FB ₂ + FC ₂ ) is preferably 4000 Hz or more, more preferably 4100 Hz or more, and further preferably 4200 Hz or more, from the viewpoint that a feeling of hitting ball can be obtained to such an extent that the player can get a sense of distance when putting.

From the viewpoint that a necessary difference (FB ₂ −FC ₂ ) is obtained, the secondary natural frequency FC ₂ of the core 4 is preferably 1700 Hz or more, more preferably 1750 Hz or more, and particularly preferably 1800 Hz or more. FC ₂ is preferably 2400 Hz or less, more preferably 2350 Hz or less, and particularly preferably 2300 Hz or less.

In light of obtaining the necessary difference (FB ₂ −FC ₂ ), the secondary natural frequency FB ₂ of the golf ball 2 is preferably 2250 Hz or higher, more preferably 2300 Hz or higher, and particularly preferably 2350 Hz or higher. FB ₂ is preferably 3050 Hz or less, more preferably 3000 Hz or less, and particularly preferably 2950 Hz or less.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
100 parts by weight of high-cis polybutadiene (trade name “BR730” from JSR), 27.8 parts by weight of zinc acrylate, 5 parts by weight of zinc oxide, an appropriate amount of barium sulfate, 0.5 parts by weight of diphenyl disulfide and 0 The rubber composition C was obtained by kneading 9 parts by mass of dicumyl peroxide. This rubber composition C was put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity and heated at 160 ° C. for 20 minutes to obtain a core having a diameter of 40.0 mm. The amount of barium sulfate was adjusted so that the mass of the golf ball was appropriate.

  40 parts by weight of ionomer resin (previously referred to as “HIMILAN AM7329”), 57 parts by weight of other ionomer resins (previously referred to as “HIMILAN 1605”), 3 parts by weight of a styrene block-containing thermoplastic elastomer (previously referred to as “Lavalon T3221C”) 4 parts by mass of titanium dioxide and 0.2 parts by mass of a light stabilizer (trade name “JF-90” from Johoku Chemical Industry Co., Ltd.) were kneaded with a twin-screw kneading extruder to obtain a resin composition c. The core was put into a final mold composed of an upper mold and a lower mold each having a hemispherical cavity. This final mold has a large number of pimples on the cavity surface. The resin composition c melted by the injection molding method was filled around the core, and a cover was molded. The cover had a thickness Tc of 1.35 mm. A dimple having a shape obtained by inverting the shape of the pimple was formed on the cover.

A clear paint based on a two-component curable polyurethane was applied around the cover to obtain a golf ball of Example 1 having a diameter of about 42.7 mm and a mass of about 45.6 g. The secondary natural frequency FB _{2 of} the golf ball and the secondary natural frequency FC _{2 of the} core measured for Example 1 are plotted as E1 in FIG.

[Example 2-18 and Comparative Example 1-4]
Golf balls of Example 2-18 and Comparative Example 1-4 were obtained in the same manner as in Example 1 except that the specifications of the core and cover were as shown in Table 4-8 below. Details of the core specifications are shown in Table 1-2 below. Details of the cover specifications are shown in Table 3 below. FB ₂ and FC ₂ measured for Examples 2-18 are plotted as E2-E18, respectively, in FIG. FB ₂ and FC ₂ measured for Comparative Example 1-4 are plotted as C1-C4 in FIG. 3, respectively.

[Approach performance: blow by wedge]
A wedge (trade name “588RTX2.0 tour satin wedge” manufactured by Cleveland, shaft hardness: S, loft angle: 52 degrees) was mounted on a swing machine manufactured by Golf Laboratory. A golf ball was hit under the condition that the head speed was 16 m / s, and the spin speed of the golf ball was measured. The average value of the values obtained by 12 measurements is shown as AP spin speed (rpm) in Table 4-8 below.

[Putter evaluation]
On a flat lawn, 10 beginners hit a golf ball with a putter toward the hitting target, and the distance (m) from the hitting point to the point where the golf ball stopped was measured. The straight line distance from the hitting point to the hitting target was 10 m. An average value is calculated by striking three balls at a time, and a value obtained by subtracting 10 m from this average value is shown as a putter evaluation (m) in Table 4-8. A positive value means that the golf ball has stopped beyond the target (overshot), and a negative value means that the golf ball has not reached the target (no hit). A golf ball having a small absolute value is highly evaluated.

[Hit feel]
On a flat lawn, 10 beginners hit a golf ball with a putter and heard the feeling. Based on the number of golfers who answered “feeling good”, the following ratings were assigned. The results are shown in Table 4-8 below as the feel at impact.
A: 9-10 people B: 7-8 people C: 5-6 people D: 0-4 people

Details of the compounds described in Table 1-2 are as follows.
BR730: JSR high cis polybutadiene (cis-1,4-bond content: 96 mass%, 1,2-vinyl bond content: 1.3 mass%, Mooney viscosity (ML _{1 + 4} (100 ° C.)): 55 Molecular weight distribution (Mw / Mn): 3)
Zinc acrylate: Sanshin Chemical Industry's trade name “Suncellor SR” (10% by mass stearic acid coating product)
Zinc oxide: Toho Zinc Co., Ltd. trade name “Ginbao R”
Barium sulfate: The trade name “Barium sulfate BD” of Sakai Chemical Co., Ltd.
Dicumyl peroxide: Nippon Oil &Fats' trade name “Park Mill D”
Diphenyl disulfide: bis (pentabromophenyl) disulfide from Kawaguchi Chemical Industries

  As shown in Table 4-8, the golf ball of each example has a good shot feeling at the time of putting. Further, the golf balls of the respective examples have small absolute values in the putter evaluation. This means that it is a ball that makes it easy for beginners to adjust the sense of distance. Further, in the golf balls of the respective examples, the spin speed at the approach shot is not significantly reduced. From this evaluation result, the superiority of the present invention is clear.

  The golf ball according to the present invention is suitable for playing on a golf course, practice in a driving range, and the like.

2 ... golf ball 4 ... core 6 ... cover 8 ... dimple 10 ... land 12 ... vibrator 14 ... plate 16 ... first acceleration pickup 18 ... Second acceleration pickup

Claims (8)

A core and a cover located outside the core;
A golf ball having a difference (FB ₂ −FC ₂ ) greater than 420 Hz and less than or equal to 760 Hz when the secondary natural frequency is FB ₂ and the secondary natural frequency of the core is FC ₂ . _2. The golf ball according to claim 1, wherein a sum (FB ₂ + FC ₂ ) of the FB ₂ and the FC ₂ is 5200 Hz or less. The golf ball according to claim 1, wherein the FC ₂ is 1700 Hz or more and 2400 or less. The golf ball according to claim 1, wherein the FB ₂ is 2250 Hz or more and 3050 Hz or less.   The golf ball according to claim 1, wherein the core has an amount of compressive deformation Dc of 2.30 mm or more and 3.90 mm or less.   6. The golf ball according to claim 1, wherein the amount of compressive deformation Db is 1.80 mm or more and 3.30 mm or less.   The golf ball according to claim 1, wherein the cover has a thickness Tc of 1.00 mm or more and 2.30 mm or less.   The golf ball according to claim 1, wherein the cover has a Shore D hardness Hc of 54 or more and 67 or less.

Images